Abstract Marriage is the central relationship for the majority of adults, and morbidity and mortality are reliably lower for the married than the unmarried. However, the simple presence of a spouse is not necessarily protective: a troubled marriage simultaneously provides a prime source of stress while limiting a partner's ability to seek support in other relationships. Marital disagreements that are marked by high rates of negative or punishing behaviors (e.g., hostility, sarcasm, withdrawal), hallmarks of marital distress, increase proinflammatory cytokine production; marital discord's notable consequences include amplified risk and poorer outcomes for inflammation-related disorders. In contrast to the negative or punishing behaviors that clearly promote marital distress, a growing literature suggests that positive marital interactions are central to satisfying relationships, and may benefit health. Capitalization behaviors (encouraging, supportive responses that follow disclosure of positive events) are among the most influential positive marital behaviors. Using three state-of-the-art molecular aging biomarkers associated with inflammation (telomere length, p16INK4a expression, and epigenetic age, the status of an individual's epigenetic clock), we address novel questions: Do unhappy marriages accelerate molecular aging? Can happy marriages slow molecular aging and extend both lifespan and health span (the length of time that a person is healthy?not just alive)? Drawing on behavioral, immunological, and molecular aging research, this study will assess concurrent and prospective relationships between key marital behaviors and molecular aging biomarkers. Accordingly, at the baseline visit, couples will be asked to resolve a disagreement, and they will also discuss positive personal events; these discussions will be behaviorally coded. Blood samples will provide data on molecular aging biomarkers in addition to couples' inflammatory responsiveness to the interactions. The couples' second visit, two years after the first, will assess changes in marital quality, inflammation, and the three molecular aging biomarkers. We have three specific aims: Aim 1: To characterize the concurrent and prospective relationships between couples' interactive behaviors and mood, inflammation, and aging biomarkers. Aim 2: To assess the relationships among inflammation and the molecular aging biomarkers. Aim 3: This exploratory aim addresses the relative contributions of gender to mood, inflammation, inflammatory responsiveness, and the aging biomarkers, as well as actor-partner effects on these outcomes. This proposal's novel methodology provides a way to test innovative and original hypotheses about the ways that marital behavior impacts lifespan and health span. The interactions among behavior, inflammation, and molecular aging represent an important new frontier for understanding how one's closest personal relationship can accelerate or slow aging. This project will help illuminate the mechanisms through which marriage influences our health and longevity -- for good or ill.